Linux Environment Variables, PATH, .bashrc and alias Explained Simply

By Ravindra Bagale, trainer LinkedIn Last updated: 25 October 2026

Every program you run gets a small bag of settings called environment variables: who you are, your home folder, where to look for commands, which editor you like, API endpoints and more. In this chapter you learn to read, set, export and remove them, how PATH finds commands, which startup file runs when, and how aliases save typing.

What you'll learn in this chapter

Read variables with echo, env and printenv
Set shell vs exported variables, and unset
Understand and change PATH safely
Use which, type and command -v
Know .bashrc, .bash_profile, /etc/profile.d and /etc/environment
Create aliases, functions and a better PS1

1. An everyday example: the school bag and the timetable

Why do we need this?

Every morning a child packs a school bag from the timetable stuck on the wall. Whatever is in the bag goes to school; things left on the table stay home. If the younger brother copies the bag, he gets the same books. And the child writes short nicknames for long subject names on the timetable.

What is it?

Timetable on the wall = .bashrc. The bag = exported environment. Things on the table = shell-only variables. Brother copying the bag = a child process inheriting env. Nicknames = aliases.

How to do it (step by step)

A new terminal tab (non-login) reads only ~/.bashrc.

2. echo $VAR: read one variable

Why do we need this?

You want to check a value quickly, like your home folder or which editor is set.

What is it?

$NAME expands to the value. Use "$NAME" in quotes to keep spaces. ${NAME:-default} gives a default if empty. Common: HOME, USER, SHELL, PWD, LANG, EDITOR, HOSTNAME, PATH.

How to do it (step by step)

Home and user.

echo "$USER lives in $HOME"

Output:

ravi lives in /home/ravi

What it means: Two variables in one line.

A default value.

echo "${EDITOR:-nano}"

Output:

nano

What it means: EDITOR was empty, so nano.

3. env and printenv: list the environment

Why do we need this?

When an app behaves differently on two servers, compare their environments.

What is it?

env and printenv list all exported variables. printenv NAME prints one (no $). env -i CMD runs CMD with an empty environment. env VAR=x CMD runs CMD with an extra variable only for that run.

How to do it (step by step)

Count and filter.

env | wc -l; env | grep -i ^lang

Output:

28
LANG=en_IN.UTF-8

What it means: 28 exported variables.

One value.

printenv SHELL

Output:

/bin/bash

What it means: No $ needed.

Run with a clean environment.

env -i /usr/bin/env

Output:

(no output)

What it means: Nothing inherited.

4. Setting variables: shell vs export

Why do we need this?

A variable you set is not seen by programs you start unless you export it. This confuses many beginners.

What is it?

NAME=value sets a shell variable (no spaces around =). export NAME or export NAME=value puts it in the environment, so child processes get it. NAME=value cmd sets it for one command only. Changes vanish when the terminal closes unless saved in a startup file.

How to do it (step by step)

Not exported.

CITY=Pune; bash -c 'echo "child sees: $CITY"'

Output:

child sees:

What it means: The child did not get it.

Exported.

export CITY=Pune; bash -c 'echo "child sees: $CITY"'

Output:

child sees: Pune

What it means: Now it is in the bag.

For one command.

TZ=Asia/Tokyo date +%H:%M; date +%H:%M

Output:

17:42
14:12

What it means: Only date's first run saw TZ.

Space mistake.

CITY = Pune

Output:

bash: CITY: command not found

What it means: No spaces around =.

5. unset and readonly

Why do we need this?

Remove a wrong or secret value from your session, or protect a value from being changed.

What is it?

unset NAME removes it from the shell and environment. export -n NAME keeps it in the shell but stops exporting. readonly NAME=value makes it constant for this shell.

How to do it (step by step)

Remove a token.

export API_TOKEN=abc123; unset API_TOKEN; echo "[${API_TOKEN}]"

Output:

[]

What it means: Gone.

Readonly.

readonly STAGE=prod; STAGE=dev

Output:

bash: STAGE: readonly variable

What it means: Protected.

6. PATH: where commands are found

Why do we need this?

'command not found' after installing a tool almost always means its folder is not in PATH.

What is it?

PATH is a list of folders separated by :. bash searches left to right and runs the first match. Add a folder: export PATH="$HOME/bin:$PATH" (front = wins) or "$PATH:/opt/tool/bin" (end). Never put . in PATH. hash -r clears bash's remembered locations.

How to do it (step by step)

See it one folder per line.

echo "$PATH" | tr ':' '\n'

Output:

/usr/local/bin
/usr/bin
/bin
/usr/local/sbin
/usr/sbin

What it means: Searched top to bottom.

Tool not found.

terraform version

Output:

bash: terraform: command not found

What it means: It is in /opt/terraform.

Add it for this session.

export PATH="$PATH:/opt/terraform" && terraform version

Output:

Terraform v1.9.8

What it means: Works now.

Make it permanent.

echo 'export PATH="$PATH:/opt/terraform"' >> ~/.bashrc && source ~/.bashrc

Output:

(no output)

What it means: Every new shell has it.

7. which, type and command -v

Why do we need this?

You type python and get the wrong version. You need to know exactly what runs.

What is it?

which NAME shows the first file in PATH. which -a shows all. type NAME tells if it is an alias, function, builtin or file (more accurate). command -v NAME is the script-safe test for 'is it installed?'.

How to do it (step by step)

All pythons.

which -a python3

Output:

/usr/local/bin/python3
/usr/bin/python3

What it means: The first one wins.

What is ll?

type ll

Output:

ll is aliased to `ls -alF'

What it means: which would not show this.

In a script.

command -v jq >/dev/null || echo 'please install jq'

Output:

please install jq

What it means: Clean check.

8. ~/.bashrc vs ~/.bash_profile

Why do we need this?

You add something and it works in a new tab but not over SSH, or the other way round. The startup file choice explains it.

What is it?

Login shells (SSH, console) read ~/.bash_profile (or ~/.profile). Interactive non-login shells (new terminal tab) read ~/.bashrc. Best practice: put everything in ~/.bashrc and make ~/.bash_profile source it. Use source ~/.bashrc (or . ~/.bashrc) to apply changes now.

File	When it runs
/etc/profile, /etc/profile.d/*.sh	Login shells, all users
~/.bash_profile or ~/.profile	Login shell, you
~/.bashrc	Every interactive shell
/etc/bashrc or /etc/bash.bashrc	Interactive, all users
/etc/environment	At login by PAM, not a script

How to do it (step by step)

Check your profile sources bashrc.

grep -n bashrc ~/.bash_profile

Output:

2:[ -f ~/.bashrc ] && . ~/.bashrc

What it means: Good, one place to edit.

Is this a login shell?

shopt -q login_shell && echo login || echo non-login

Output:

login

What it means: SSH sessions are login shells.

Apply changes now.

source ~/.bashrc

Output:

(no output)

What it means: No need to log out.

9. /etc/environment and /etc/profile.d

Why do we need this?

A proxy or a company tool path must be set for every user on the server, not only you.

What is it?

/etc/environment holds plain KEY=value lines (no export, no $VAR expansion), read at login. /etc/profile.d/NAME.sh is a script run by login shells for all users; you can use export and $PATH there. systemd services do not read these; use Environment= in the unit.

How to do it (step by step)

Company proxy for all.

echo 'https_proxy=http://proxy.corp:3128' | sudo tee -a /etc/environment

Output:

https_proxy=http://proxy.corp:3128

What it means: Plain line, no export.

Tool path for all.

echo 'export PATH="$PATH:/opt/terraform"' | sudo tee /etc/profile.d/terraform.sh

Output:

export PATH="$PATH:/opt/terraform"

What it means: Works after next login.

A service needs a variable.

sudo systemctl edit shop-api
[Service]
Environment=NODE_ENV=production

Output:

(override saved)

What it means: Services ignore .bashrc.

10. alias and unalias

Why do we need this?

You type the same long commands every day. An alias makes them short and adds safety flags.

What is it?

alias NAME='command' creates one. alias alone lists all. unalias NAME removes it. Save in ~/.bashrc to keep. \NAME or command NAME runs the real command, skipping the alias. Aliases do not work in scripts by default.

How to do it (step by step)

Short and safe.

alias ll='ls -lh' rm='rm -i' k='kubectl'

Output:

(no output)

What it means: rm now asks first.

List.

alias | head -3

Output:

alias k='kubectl'
alias ll='ls -lh'
alias rm='rm -i'

What it means: Your shortcuts.

Skip the alias once.

\rm old.log

Output:

(no output)

What it means: No question this time.

Remove.

unalias k && type k

Output:

bash: type: k: not found

What it means: Gone.

11. Shell functions for bigger shortcuts

Why do we need this?

Aliases cannot take arguments in the middle. Functions can, and can run several steps.

What is it?

NAME() { commands; } in ~/.bashrc. $1, $2 are arguments, "$@" is all. declare -f NAME shows it. unset -f NAME removes it.

How to do it (step by step)

Make a folder and enter it.

mkcd() { mkdir -p "$1" && cd "$1"; }; mkcd /tmp/demo && pwd

Output:

/tmp/demo

What it means: One word, two steps.

Tail a service's logs.

logs() { journalctl -u "$1" -n "${2:-50}" --no-pager; }; logs nginx 5

Output:

(5 nginx log lines)

What it means: Default 50 lines.

12. PS1: a prompt that helps

Why do we need this?

Typing a command on the production server by mistake is a classic outage. A clear prompt shows where you are.

What is it?

PS1 sets the prompt. \u user, \h host, \w folder, \$ shows # for root. Colours with \[\e[31m\] (red) and \[\e[0m\] (reset). Put it in ~/.bashrc.

How to do it (step by step)

Simple.

PS1='\u@\h:\w\$ '

Output:

ravi@web1:~/app$

What it means: User, host, folder.

Red PROD tag.

PS1='\[\e[41m\]PROD\[\e[0m\] \u@\h:\w\$ '

Output:

PROD ravi@db1:~$

What it means: You cannot miss it.

13. HISTSIZE, HISTCONTROL and history tricks

Why do we need this?

History saves you from retyping and helps you recall what you did during an incident.

What is it?

HISTSIZE (in memory) and HISTFILESIZE (in ~/.bash_history) set how much to keep. HISTCONTROL=ignoreboth skips duplicates and lines starting with a space (use a leading space for secrets). HISTTIMEFORMAT='%F %T ' adds times. history, !N, Ctrl+R to search.

How to do it (step by step)

Better history settings.

cat >> ~/.bashrc <<'X'
HISTSIZE=10000
HISTFILESIZE=20000
HISTCONTROL=ignoreboth
HISTTIMEFORMAT='%F %T '
X

Output:

(no output)

What it means: Big, clean, timed history.

With times.

source ~/.bashrc; history 2

Output:

  501  2026-10-25 14:20:11 source ~/.bashrc
  502  2026-10-25 14:20:14 history 2

What it means: When you ran it.

14. Real examples from many industries

Why do we need this?

The same Linux skill shows up in every kind of company. Seeing it in many places helps you remember it.

What is it?

Each row is a made-up team. It shows who uses this and how.

How to do it (step by step)

Team and city	How they use it	Command
Shruti, fintech, Pune	Red PROD prompt on payment servers	`PS1='PROD \u@\h:\w\$ '`
Jack, game studio, Austin	Adds the SDK to PATH for all users	`/etc/profile.d/sdk.sh`
Leila, airline, Abu Dhabi	Sets proxy via /etc/environment	`https_proxy=http://proxy:3128`
Pedro, logistics, Lisbon	k alias for kubectl	`alias k=kubectl`
Arjun, data team, Bengaluru	Picks the right python with which -a	`which -a python3`
Nina, SaaS, Stockholm	Service env via Environment=	`Environment=NODE_ENV=production`

15. Common errors and how to fix them

Why do we need this?

Everyone hits these errors. Knowing the cause saves hours.

What is it?

Read the exact message first. Then match it to a row below.

How to do it (step by step)

Error you see	Why it happens	How to fix
`bash: terraform: command not found`	Folder not in PATH	Add it to PATH. `export PATH="$PATH:/opt/terraform"`
`bash: CITY: command not found (after CITY = Pune)`	Spaces around =	Write NAME=value. `CITY=Pune`
`Child program does not see the variable`	Not exported	export it. `export CITY`
`Change in .bashrc not working over SSH`	Login shell reads .bash_profile, which does not source .bashrc	Source .bashrc from .bash_profile. `echo '. ~/.bashrc' >> ~/.bash_profile`
`ls: command not found (every command broken)`	PATH was overwritten, not appended	Restore PATH, fix the line. `export PATH=/usr/local/bin:/usr/bin:/bin`
`Service ignores my variable`	systemd does not read .bashrc	Use Environment= or EnvironmentFile=. `sudo systemctl edit shop-api`
`bash: STAGE: readonly variable`	It was made readonly	Open a new shell. `bash`
`Old version still runs after install`	bash hash cache or earlier PATH entry	Clear the hash and check order. `hash -r; which -a node`
`Alias works in terminal but not in script`	Aliases are off in non-interactive shells	Use the full command or a function. `command -v kubectl`
`sudo: mytool: command not found`	sudo uses secure_path, not your PATH	Use the full path. `sudo /opt/mytool/bin/mytool`

16. Troubleshooting step by step

Why do we need this?

When a command or variable is not what you expect, check what bash sees, step by step.

What is it?

Go top to bottom. Stop at the first step that shows the problem.

How to do it (step by step)

What is it?

type -a mytool

Where does PATH look?

echo "$PATH" | tr ':' '\n'

Is the variable set and exported?

declare -p MYVAR; printenv MYVAR

Which startup files ran?

shopt -q login_shell && echo login; grep -n bashrc ~/.bash_profile

Who sets it?

grep -rn MYVAR ~/.bashrc ~/.bash_profile /etc/profile.d /etc/environment 2>/dev/null

Test in a clean shell.

env -i bash -l -c 'echo $PATH'

17. Lab 1: Variables, export and PATH

Why do we need this?

See the difference between shell and exported variables, then add your own bin folder to PATH permanently.

What is it?

A full hands-on lab. Run every step on a test Linux machine (an EC2 instance, a VM, or WSL).

How to do it (step by step)

Shell vs export.

A=1; export B=2; bash -c 'echo A=$A B=$B'

Output:

A= B=2

Make a script in ~/bin.

mkdir -p ~/bin && printf '#!/bin/bash\necho hello from bin\n' > ~/bin/hi && chmod +x ~/bin/hi

Output:

(no output)

Not found yet?

hi

Output:

bash: hi: command not found (or it works if ~/bin is already in PATH)

Add to PATH permanently.

echo 'export PATH="$HOME/bin:$PATH"' >> ~/.bashrc && source ~/.bashrc && hi

Output:

hello from bin

Check order.

type -a hi; echo "$PATH" | tr ':' '\n' | head -n1

Output:

hi is /home/ravi/bin/hi
/home/ravi/bin

18. Lab 2: Aliases, a function and a safe prompt

Why do we need this?

Add aliases and a function to ~/.bashrc, a coloured prompt, and better history.

What is it?

A full hands-on lab. Run every step on a test Linux machine (an EC2 instance, a VM, or WSL).

How to do it (step by step)

Back up .bashrc.

cp ~/.bashrc ~/.bashrc.bak

Output:

(no output)

Add aliases and a function.

cat >> ~/.bashrc <<'X'
alias ll='ls -lh'
alias rm='rm -i'
mkcd() { mkdir -p "$1" && cd "$1"; }
PS1='\[\e[32m\]\u@\h\[\e[0m\]:\w\$ '
HISTCONTROL=ignoreboth
X

Output:

(no output)

Load and test.

source ~/.bashrc && type ll && mkcd /tmp/lab24 && pwd

Output:

ll is aliased to `ls -lh'
/tmp/lab24

Skip an alias.

touch x && \rm x && echo removed

Output:

removed

Restore if you like.

cp ~/.bashrc.bak ~/.bashrc && source ~/.bashrc

Output:

(no output)

Ravindra Bagale's Tip

When you change PATH, always keep $PATH in the new value, and back up ~/.bashrc first. One wrong line like PATH=/opt/tool breaks every command, and then you have to type full paths like /usr/bin/vi to fix it.

19. Frequently asked questions

Q. export vs no export?

Without export, only this shell sees it. With export, programs it starts see it too.

Q. Why did my variable disappear?

It was set only in that terminal. Save it in ~/.bashrc.

Q. Front or end of PATH?

Front to override system tools, end to add new ones safely.

Q. which vs type?

type knows aliases, functions and builtins; which only files.

Q. Do I need to log out after editing .bashrc?

No, run source ~/.bashrc.

Q. Where should secrets go?

Not in .bashrc or history. Use a secrets manager or a root-only EnvironmentFile.

Q. What about zsh?

Same ideas; files are ~/.zshrc and ~/.zprofile.

Q. Why does sudo not find my command?

sudo uses secure_path from sudoers. Use the full path.

20. Interview questions and answers

Beginner level

Q. How do you see all environment variables?

env or printenv.

Q. How do you set a variable for child processes?

export NAME=value.

Q. What is PATH?

The list of folders searched for commands.

Q. How do you create an alias?

alias ll='ls -lh'.

Mid level level

Q. .bashrc vs .bash_profile?

bashrc for every interactive shell; bash_profile for login shells, usually sources bashrc.

Q. How do you find which binary runs?

type -a or which -a.

Q. Set a variable for all users?

/etc/environment or /etc/profile.d/*.sh.

Q. Run one command with a different variable?

VAR=value command.

Senior level

Q. Why is '.' in PATH dangerous?

A malicious file named like a common command in the current folder could run.

Q. Env vars and twelve-factor apps?

Config in env, not code; inject per environment; keep secrets out of images and logs.

Q. Why might a cron job and an SSH session have different PATH?

cron does not read profiles; it uses a minimal environment.

Q. How do you debug slow shell start-up?

bash -x -l -c exit or time bash -i -c exit; look for slow lines in rc files.

Try at home

Write three aliases you would really use and one function that takes an argument. Put them in ~/.bashrc and show type output for each.
Print your PATH one folder per line and explain where each folder came from.

Practice Tasks

About this scenario

Ahmednagar Sugar Co-op is a sugar co-operative business in Ahilyanagar. Balasaheb Pawar looks after its IT and cloud work. They count money in INR and run their AWS resources in the ap-south-1 Region. In the tasks below you do real jobs for them using what this lesson teaches. All names, account IDs, IP addresses and numbers are made up for practice.

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